The mammal which was harpooned and slaughtered by the Icelandic whaling company Hvalur hf on July 7 was a hybrid of a blue whale and a fin whale.

Iceland is the only country where it is legal to hunt the fin whale, despite an international moratorium on whaling.

“According to the (hunting) licence, whaling is limited to fin whales and there is no exception,” Ragnar Adalsteinsson, the lawyer representing the wildlife and nature conservation group Jardarvinir, told AFP.

He said the group had asked that Iceland’s public prosecutor look into whether the nation’s whaling laws had been violated.

“The request is that the matter should be investigated and if criminality is confirmed, the company should go before a court,” Adalsteinsson said.

The killing of what was first believed to be an endangered blue whale triggered outrage among anti-whaling groups as the animal has been protected by the International Whaling Commission since 1966.

But a DNA test later showed that the butchered mammal was in fact a hybrid of a fin whale and a blue whale.

Scientists say such hybrids are very rare, possibly even rarer than the blue whales.

Since 1983, five such whales have been observed in Icelandic waters and they are known to be infertile.

All whales killed in Iceland undergo DNA tests after the hunting season.

Hvalur hf had initially argued that the whale was a fin whale. Contacted by AFP, they were not immediately available for comment.